As described in the patent document 1, electromagnetic noise is shielded using a radio-frequency filter as the technology of electronic circuit board for improving the electromagnetic interference preventing function in the prior art.
[Patent document 1]
Japanese Unexamined Patent Publication No. Hei 05(1993)-259686
In the prior art, it is still required to prevent malfunction of an electronic circuit due to electromagnetic noise of higher frequency and larger output level. In order to overcome this requirement described above, malfunction can be prevented by adding a capacitor and an inductor. However, the electronic circuit board becomes too large to satisfy the requirement for reduction in size. Moreover, addition of capacitor and inductor will cause a problem of rise in cost due to increase in number of components.